The president's bold move set off waves of criticism from Republican lawmakers, many of whom had demanded to know whether the White House made the appointment without consulting the Justice Department's Office of Legal Counsel, a critical arbiter of the constitution for the executive branch.

But in an Office of Legal Counsel memo dated Jan. 6 and released earlier today, Assistant Attorney General Virginia A. Seitz writes that a survey of the U.S. Constitution and precedent support the idea that the Senate's short pro forma sessions do not interrupt a true recess. So, "the president therefore has discretion to conclude the Senate is unavailable to perform its advise-and-consent function and to exercise his power to make recess appointments."

The Recess Appointments Clause of the Constitution gives the president the power to fill vacancies during Senate breaks — but the fighting over the Cordray appointment boils down to the meaning of the word "recess" — and whether the minute-long sessions led by a single senator, often during the holidays, count as real work periods under the meaning of the law. The U.S. Supreme Court has never addressed the issue directly but Harvard Law Professor Lawrence Tribe told NPR last week that he expected possible litigation by businesses who are regulated by Cordray could make its way all the way up to the nation's highest court.